Validation of Contour Advection simulations with airborne lidar measurements of filaments during the Second European Stratospheric Arctic and Midlatitude Experiment (SESAME)

Airborne lidar measurements of vertical sections of ozone and aerosol across the lower stratospheric vortex boundary during the Arctic winter 1994/1995 are used to study the permeability of this dynamical barrier. Both constituents exhibit strong gradients in the lower levels of the vortex edge and substantial structure at subsynoptic scales in the surrounding surf zone. These measurements provide validation of two-dimensional (2-D) Contour Advection (CA) calculations which use potential vorticity (PV) as a proxy tracer. The CA calculations are initialized from gridded U.K. Meteorological Office analyses and thus may smooth subgrid scale structures. Contour Advection reproduces most of the observed filaments with an accuracy of few tenths of a degree, but neglect of diabatic effects causes small errors. The CA calculations show that the arctic stratosphere was dynamically disturbed over extended periods by breaking planetary waves as indicated by numerous spiral-like PV filaments which surrounded the polar vortex. The transport rate across the vortex boundary due to filamentation and subsequent detachment of the filaments off the vortex can be inferred from the model calculations. In winter 1994/1995, two wave breaking events eroded the area of the Arctic vortex by 8% and 40% at 450 K and by 22% and 60% at 600 K. A third event triggered off the final warming. Since the vortex air partly was chemically disturbed, this cross vortex boundary transport, together with effective catalytic ozone destruction cycles, has considerable potential for reducing ozone concentrations at midlatitudes.